The present invention relates to a hydraulic drive apparatus for a working machine which transmits an output torque of a plurality of hydraulic motors to an output shaft.
In conventional, in a working machine such as a wheel loader or the like, there has been known a hydraulic drive apparatus which transmits an output torque of a plurality of hydraulic motors to an output shaft.
FIG. 9 is a skeleton view of a hydraulic drive apparatus disclosed in Unexamined Japanese Patent Publication No. 2000-193065. In FIG. 9, a hydraulic drive apparatus 1 is provided with an output shaft 2 connected to a load 20, an output gear 3 adhered to the output shaft 2, a first input gear 4 engaged with the output gear 3, a first input shaft 5 to which the first input gear 4 is adhered, a second input gear 6 engaging with the first input gear 4, and a second input shaft 7 to which the second input gear 6 is adhered. The output gear 3, the first input gear 4 and the second input gear 6 are respectively spur gears.
A first hydraulic motor 8 having a high vehicle speed and a low torque and a control pump 9 are respectively connected to one end side portion of the first input shaft 5 and another end side portion thereof. Further, a second hydraulic motor 11 having a low vehicle speed and a high torque is connected to an axial end portion of the second input shaft 7 via a clutch 10.
The first hydraulic motor 8 and the second hydraulic motor 11 are connected to a hydraulic pump (not shown) via a hydraulic parallel circuit and are driven by a discharged pressurized oil thereof.
The clutch 10 is normally in an engaging state due to an urging force of a spring 12 and is broken down in accordance that a clutch oil pressure P3 supplied from an oil pressure source via an oil passage 13 becomes greater than the urging force. The clutch oil pressure P3 is controlled to be supplied or broken down by a two position switching valve 14 interposed in the oil passage 13.
An orifice 16, a check valve 17 and a relief valve 18 are arranged in parallel in a discharged oil passage 15 of the control valve 9. When an oil pressure P1 of the discharged oil passage 15 detected by the orifice 16 is over a set oil pressure, a pilot pressure is supplied to the two position switching valve 14 and the two position switching valve 14 is opened, whereby the clutch oil pressure is applied and the clutch 10 is broken down.
At a time of low speed traveling, the clutch 10 is in an engaging state, both of the first hydraulic motor 8 and the second hydraulic motor 11 are connected to the output shaft 2, thereby driving the load 20 at a high torque. Further, at a time of high speed traveling, a discharge amount of the control pump 9 is increased in accordance with an increase of a rotational number of the first hydraulic motor 8. Further, when the oil pressure of the discharged oil passage 15 detected by the orifice 16 becomes over the set oil pressure, a pilot pressure P2 is supplied to the two position switching valve 14. Accordingly, the two position switching valve 14 is opened, the clutch 10 is broken down in accordance with the clutch oil pressure P3, and the torque is transmitted to the output shaft 2 from only the first hydraulic motor 8, thereby driving the load at a high speed.
Further, at a time of changing to the low speed traveling from the high speed traveling, the discharge amount of the control pump 9 is reduced in correspondence to a reduction of the rotational speed of the first hydraulic motor 8. Accordingly, the pilot pressure P2 supplied to the two position switching valve 14 is reduced and the two position switching valve 14 is closed. As a result, the clutch oil applied to the clutch 10 at the clutch pressure P3 passes to a drain 34 through a drain line 23 from the two position switching valve 14, and the clutch pressure P3 is reduced to be lower than the urging force of the spring 12, whereby the clutch 10 in a broken state is engaged due to the urging force.
However, in accordance with the prior art mentioned above, there are the following problems.
That is, in accordance with an arrangement of the prior art, the spur gear is used for the output shaft 2, and the first input shaft 5 and the second input shaft 7 are connected thereto. In the spur gear, it is necessary to largely change a size between axes and an outer diameter in order to change a speed reduction ratio, so that a freedom of setting a speed reduction gear of the first and second hydraulic motors 8 and 11 with respect to the output shaft 2 is low. Accordingly, there is a problem that it is hard to set an optimum speed reduction ratio with respect to each of the hydraulic motors 8 and 11.
Further, since the second input shaft 1 is connected to the output shaft 2 via the first input shaft 5, it is necessary to arrange a center axis of the first input shaft 5 in a left portion (or a right portion) of a center axis of the output shaft 2 and arrange a center axis of the second input shaft 7 in a further left portion (or a further right portion) thereof, so that the hydraulic drive apparatus is shifted in a lateral direction. Accordingly, in a working vehicle in which it is necessary to arrange the output shaft 2 at a substantially center in a lateral direction of the vehicle, for example, an articulate type working vehicle, there is a problem that a size of the hydraulic drive apparatus 1 in a lateral direction of the vehicle is increased and it is hard to mount in the working vehicle.
Further, since the second hydraulic motor 11 is connected onto the second input shaft 7 via the clutch 10, the second input gear 6 and the clutch 10 are coaxially arranged, and an axial length of the second input shaft 7 is increased. Accordingly, there is a problem that the size of the hydraulic drive apparatus 1 is caused to be increased.
Further, since the clutch 10 is provided in the second input shaft 7 having a high peripheral speed, a difference of the rotational numbers between both side of the clutch 10 is large at a time of engaging the clutch 10. Accordingly, there is a problem that an abrasion is easily generated in the clutch 10 and a shock is great at a time of engaging.
Here, FIG. 10 shows a change with the passage of time of the clutch pressure P3 at a time of changing from the high speed traveling to the low speed traveling. The clutch oil applied to the clutch 10 from a time t1 when the two position switching valve 14 is opened passes to the drain 34 at a substantially fixed flow rate through the two position switching valve 14 and the drain line 23. In accordance therewith, the clutch pressure P3 is reduced in accordance a with a substantially fixed incline, and the clutch 10 is engaged at a time t2 when the clutch pressure P3 reaches a predetermined pressure PC.
At this time, when reducing a flow rate at which the clutch oil passes to the drain 34, a long time is required for engaging the clutch 10, so that the working vehicle can not obtain a torque required at a desired timing and a travel and an operation become unstable. Accordingly, it is necessary to set the flow rate at which the clutch oil passes to a level equal to or more than a predetermined flow rate.
However, when setting the flow rate at which the clutch oil passes to the level equal to or more than the predetermined flow rate, the clutch pressure P3 is suddenly reduced and a magnitude thereof becomes smaller than the urging force of the spring 12, so that the clutch 10 is suddenly engaged. Accordingly, a great engagement shock is generated at a time of engaging the clutch 10, whereby an uncomfortable ride of the working vehicle is generated, and a load is applied to the clutch 10 due to the sudden engagement, whereby a service life of the clutch 10 is reduced.
That is, in accordance with the prior art, there is a problem that there is no means for softening the shock at a time of engaging the clutch.
The present invention is made by paying attention to the problems mentioned above, and an object of the present invention is to provide a hydraulic drive apparatus which can obtain a desired speed reduction ratio, is compact and has a small shock at a time of engaging.
In order to achieve the object mentioned above, in accordance with a first aspect of the present invention, there is provided a hydraulic drive apparatus for a working machine having, variable capacity type first hydraulic motor and second hydraulic motor, a first input shaft connected to the first hydraulic motor, and a second input shaft freely engaged with the second hydraulic motor, the hydraulic drive apparatus transmitting an output torque of the first hydraulic motor and the second hydraulic motor to an output shaft, wherein the output shaft is connected to the first input shaft, the output shaft is connected to the second input shaft respectively via a train of gears, a planetary gear is interposed between the second hydraulic motor and the second input shaft, and a clutch freely engaging the second hydraulic motor with the second input shaft is provided between the second hydraulic motor and the planetary gear.
In accordance with the first aspect of the present invention, the first input shaft is connected to the output shaft and the second input shaft are connected to the output shaft, respectively without disposing the other shaft therebetween. Accordingly, it is possible to independently set a speed reduction ratio of the first input shaft and the second input shaft with respect to the output shaft, respectively. Accordingly, for example, since it is possible to set a speed reduction ratio respectively suitable for the first hydraulic motor having a high vehicle speed and a low torque and the second hydraulic motor having a low vehicle speed and a high torque, a torque transmitting efficiency of the hydraulic motor is improved and a drive efficiency of the working vehicle is improved.
Further, the planetary gear is interposed between the second hydraulic motor and the second input shaft. Accordingly, since the speed reduction ratio from the second hydraulic motor to the output shaft is increased, a great torque is generated, so that it is possible to make the second hydraulic motor compact. Further, since the planetary gear can change the speed reduction ratio without largely changing an outer diameter, the planetary gear can set an optimum speed reduction ratio with respect to the hydraulic motor within a limited internal space of the working vehicle. For example, even when the specification of the existing hydraulic motor does not have a torque characteristic required for the working vehicle, a desired torque can be obtained.
Further, the clutch freely engaging the second hydraulic motor with the second input shaft is provided between the second hydraulic motor and the planetary gear. Accordingly, it is possible to damp a shock generated at a time of engaging the clutch. For example, when the clutch is provided between a ring gear and a housing of the hydraulic drive apparatus, a difference of speed with respect to the housing becomes small since the ring gear has a low peripheral speed, so that an abrasion generated at a time of engaging the clutch becomes small and a service life of the clutch becomes long. Further, since the difference of speed at a time of engaging the clutch is small, an engaging shock becomes small and a comfortable feeling for driving in improved.
In accordance with a second aspect of the present invention, there is provided a hydraulic drive apparatus for a working machine as cited in the first aspect, wherein center axes of the first input shaft and the second input shaft are arranged in left and right upper portions of the center axis of the output shaft in a symmetrical manner.
In accordance with the second aspect of the present invention, with respect to the output shaft arranged at a substantially center portion in a lateral direction of the working vehicle, the first and second input shafts are respectively arranged in left and right upper portions of the output shaft in a substantially symmetrical manner. Accordingly, the hydraulic drive apparatus is not shifted with respect to the center in the lateral direction of the working vehicle, a weight balance in the lateral direction is improved. Further, since a size of the hydraulic drive apparatus with respect to the center of the working vehicle is equalized, it becomes easy to receive the hydraulic drive apparatus within the working vehicle.
In accordance with a third aspect of the present invention, there is provided a hydraulic drive apparatus for a working machine as cited in the first aspect, wherein a lubricating oil port for taking in a lubricating oil is provided in an end portion of the second input shaft opposite to the second hydraulic motor.
In accordance with the third aspect of the present invention, the lubricating oil port is provided in the second input shaft, and the lubricating oil is taken in therefrom so as to lubricate the planetary gear. Accordingly, in comparison with lubricating means structured such as to soak the planetary gear within an oil tank, a drive force loss at a time when the planetary gear mixes the lubricating oil within the oil tank is reduced, and an energy efficiency of the working vehicle is improved.
In accordance with a fourth aspect of the present invention, there is provided a hydraulic drive apparatus for a working machine as cited in the first, second or third aspect, wherein the clutch is a negative clutch and a modulation damper for preventing a clutch oil pressure from being suddenly taken out is provided in a drain line for taking out the clutch oil pressure of the clutch.
In accordance with the fourth aspect of the present invention, the clutch is set to the negative clutch. Accordingly, since the clutch is always in an engaging state even in the case that the engine and the hydraulic pump stop during the travel, the hydraulic pump becomes a brake so as to reduce the speed of the working vehicle.
Further, the modulator damper for preventing the clutch oil pressure from being suddenly taken out is provided in the drain line for taking out the clutch oil pressure of the clutch. Accordingly, the clutch is not suddenly engaged and the shock at a time of engaging is reduced, whereby a ride feeling of the working vehicle is improved.
In accordance with a fifth aspect of the present invention, there is provided a hydraulic drive apparatus for a working machine as cited in the first or second aspect, wherein a control pump for controlling the clutch oil pressure is connected to an end portion of the first input shaft opposite to the first hydraulic motor.
In accordance with the fifth aspect of the present invention, the control pump for controlling the clutch oil pressure is connected to the first input shaft for connecting the first hydraulic motor. Accordingly, since a shaft or a gear for driving the control pump is not independently required, the structure of the hydraulic drive apparatus for the working machine becomes simple and compact.
In accordance with a sixth aspect of the present invention, there is provided a hydraulic drive apparatus for a working machine having, first hydraulic motor and second hydraulic motor, a first Input shaft connected to the first hydraulic motor, a second input shaft connected to the second hydraulic motor so as to be freely engaged by a clutch being controlled by a switching valve, and an output shaft connected to the first input shaft and the second input shaft via a gear train, the hydraulic drive apparatus transmitting an output torque of the first hydraulic motor and the second hydraulic motor to the output shaft, wherein a modulation damper for suddenly reducing the clutch pressure before engagement and slowly reducing the clutch pressure at a time of engagement is provided in a drain line of the switching valve.
In accordance with the sixth aspect of the present invention, the modulation damper for slowly reducing the clutch pressure is provided in the drain line for taking out the clutch pressure of the clutch.
Accordingly, since the clutch pressure is slowly reduced before the clutch is engaged, a magnitude of the clutch pressure and a magnitude of the spring urging force are gradually close to each other, and the clutch is not suddenly engaged. Therefore, a shock at a time of engagement can be reduced, a service life of the clutch can be increased, and a ride feeling of the working vehicle can be improved. Further, since the structure is made such that the clutch pressure is suddenly reduced before the clutch is engaged, a long time is not required before the clutch is engaged, so that it is possible to engage the clutch at a desired timing. Accordingly, no trouble is generated for traveling the working vehicle, and a stable operation can be performed.
In accordance with a seventh aspect of the present invention, there is provided a hydraulic drive apparatus for a working machine as cited in the sixth aspect, further comprising a control pump driven by the first hydraulic motor via the first input shaft or the gear train, and a two position switching valve for controlling an engagement of the clutch on the basis of an oil pressure discharged by the control pump.
In accordance with the seventh aspect of the present invention, the control pump for controlling the clutch pressure is driven by the first hydraulic motor, and the engagement and disengagement of the clutch is controlled by the oil pressure discharged from the control pump. Accordingly, the hydraulic drive apparatus controls the engagement and disengagement of the clutch in correspondence to the rotational speed of the first hydraulic motor, that is, the speed of the working vehicle, so that it is possible to always control the clutch at a timing suitable for the travel of the working vehicle.
Further, since it is possible to constitute the hydraulic drive apparatus only by the hydraulic circuit and an electrical control system such as a controller or the like is not required, the structure of the hydraulic drive apparatus for the working machine can be made simple and compact.